They are good gears, but longevity varies.
For example, I bought my boat with about 3400 hours. After the first season, I decided to rebuild the tranny. It shifted and sounded fine, but I am a little anal sometimes.
The clutch surfaces were disintegrating. The reverse cylinder had some rust on the top portion which eventually would have broken (happened to a friend of mine).
So I decided to rebuild it myself. Easy work, had to but a manual, some snap ring pliers, borrow a large socket, not bad.
I decided to replace the two bearings, they inspected ok but since I had it apart why not. (the bearings were the expensive parts).
I even paid to have it bench tested before I reinstalled it.
All in all it cost me about $500. After 11 seasons and about 1400 hours still holding up.